Spatial subsidies and indirect effects in subarctic food webs

捕食者和猎物之间的相互作用往往受到群落中其他物种的存在和密度的影响。共有捕食者的物种可以通过共同捕食者捕食的变化间接影响彼此的丰富度。我的研究项目试图了解食物网中的这种间接互动，特别是捕食者和猎物之间的互动是如何受到替代食物来源的影响的。我特别感兴趣的是，当种群以规律的周期波动时，以及当陆地捕食者的替代食物来源来自海洋环境时，这些间接影响。当它们的主要猎物旅鼠减少时，北极狐狸经常增加对鹅的捕食压力。冬季和春季的北极狐也以海冰上的海豹为食，当海豹的可获得性和北极熊的身体状况(反映海豹的可及性)很高时，北极狐狸的数量可能会增加。由海豹补贴的北极狐狸捕食增加是否会抑制旅鼠的数量或鹅的繁殖仍有待测试。这项研究将调查海洋环境(海豹和北极熊)的变化如何通过北极狐在马尼托巴省北部哈德逊湾西缘的捕食影响陆地食草动物(鹅和旅鼠)。我们将通过夏季的洞穴调查来监测北极狐数量的年度变化，通过春季冰面上的航空调查来监测海豹的可获得性，使用标记-重新捕获的方法监测旅鼠的丰度，以及通过巢调查来监测鹅对蛋的捕食。旅鼠和狐狸的饮食变化将通过稳定同位素和粪便分析来确定，旅鼠对苔原植被的任何级联影响将通过封闭来确定。随着气候变暖和海冰减少，这项研究将试图了解海洋资源的减少可能如何影响陆地食草动物的生产力和循环旅鼠的动态。由于捕食和食草是构建生态群落的关键生态过程，本建议中描述的研究(与该地区的其他长期研究合作)将为理解亚大气层中的食物网相互作用提供基本信息。

Interactions between predators and their prey are often affected by the presence and density of other species in the community. Species that share a predator can affect each others' abundance indirectly through changes in predation by the common predator. My research program seeks to understand such indirect interactions in food webs, particularly how interactions between predators and their prey are affected by alternative food sources. I am particularly interested in understanding these indirect effects when populations fluctuate in regular cycles, and when the alternative food source for a terrestrial predator comes from the marine environment. Arctic foxes often increase predation pressure on geese when their primary prey, lemmings, decline. Arctic foxes in winter and spring also feed on seals on the sea ice and can increase in abundance when seal availability and polar bear body condition (reflecting accessibility of seals) are high. Whether increased predation by arctic foxes subsidized by seals can suppress lemming populations or goose reproduction remains to be tested. This research will investigate how changes in the marine environment (seals and polar bears) affect terrestrial herbivores (geese and lemmings) through predation by arctic fox on the west edge of Hudson Bay in northern Manitoba. We will monitor annual changes in arctic fox abundance through den surveys in summer, seal availability through aerial surveys on the ice in spring, lemming abundance using mark-recapture methods, and egg predation on geese using nest surveys. Changes in diets of lemmings and foxes will be determined through stable isotope and fecal analysis, and any cascading effects of lemmings on tundra vegetation will be determined using exclosures. As the climate warms and sea ice declines, this research will seek to understand how a decline in marine resources may affect terrestrial herbivore productivity and dynamics of cyclic lemmings. As predation and herbivory are key ecological processes structuring ecological communities, the research described in this proposal (in collaboration with other long-term research in the area) will provide information fundamental to understanding the food web interactions in the subaractic.